Pneumatic actuator



United States Patent 1 1 3,525,289

[72] Inventor Ettore C. Cercone [56] References Cited Flushing. New YorkUNITED STATES PATENTS I211 P 800,231 2,507,254 5/1950 Jones 74/531x [221Fflcd 2,840,094 6/1958 Taplin 92/48 [451 Minted 3,103,855 9/1963 Hagereta1. 92/98x [731 Assgnee Umed f 3 116 918 1/1964 Francis 92/49x East f g3,152,518 10/1964 AyersJr. 92/49x e aware 3,410,779 11/1968 Whiteheadetal 92/98X FOREIGN PATENTS 1,213,363 1/1959 France 92/49 PrimaryExaminer Martin P. Schwadron Assistant Examiner- Leslie J. Payne [54]PNEUMATIC ACTUATOR Attarney- Edmund C. Me1s1nger 3 Claims, 1 DrawingFig.

[52] U.S.Cl 92/49, ABSTRACT: An actuator is disclosed wherein ahalf-area 92/98, 92/99, 92/100 piston assembly traverses a fixed shaft.The piston assembly [51] 1nt.Cl Fl6j 3/00, consists of two pistonshaving overlying rolling diaphragms F01b 19/00 fixed at the peripheriesto the housing. The pistons are cou- [50] Field of Search 92/98, pled bya sleeve which slides over the fixed shaft. The actuator 98RD, 99, 100,48, 49; 91/369, 369A, 369B;

converts axial motion to rotary motion in a compact assembly andprovides a shorter actuator for given stroke.

PNEUMATIC ACTUATOR BACKGROUND OF THE INVENTION This invention relates topneumatic actuators and more specifically pertains to an improvedpneumatic actuator assembly designed to convert linear motion intorotary motion.

It is known to provide actuators for operating valves which are operatedby rotation of the valve about a central shaft. Typically, actuators forthis purpose feature a piston and a shaft assembly which reciprocate asa unit. The actuator has to include clearance for the moving shaft and,as a result, a

longer and heavier actuator is required. Previously proposedactuatorshaving a piston sliding on a central bar for translating linear motioninto rotation have been proposed but have not been fully satisfactory.Since there was no positive seal in the prior art actuators, a certainamount of leakage was experienced at the periphery of the piston.Furthermore, the prior art actuators required a pressure differentialacross the piston in order to provide the rotary motion because theeffective area ratio across the piston could not be simply varied. Inmany applications, significant benefits are realized by actuating avalve against a high back pressure where the servo-controlled actuatingpressure is lower than the back pressure.

SUMMARY OF THE INVENTION It is an object of this invention to provide animproved actuator for converting linear motion into rotary motion.

Another object of this invention is the provision of a pneumaticactuator consisting of a piston assembly with different effective areasguided by a fixed shaft. Another aspect of this invention lies in thenesting of the rolling diaphragms to provide a compact piston assembly.

In accordance with the invention, a piston assembly is disposed upon asleeve which translates on a fixed longitudinal shaft. The pistonassembly consists of a large inverted cup piston and an elongatedsmaller cup piston disposed in part within the large piston and bothpistons have a rolling diaphragm overlying the outer base walls. Thesleeve locates the piston assembly concentric with the fixed shaft andcouples the two pistons into a unitary assembly. A cylinder guide,interposed between the pistons, provides a rolling surface for thediaphragm associated with the smaller cup piston. A link connects thepiston assembly to a crank on a transversely located rotatable shaft forconverting linear motion to rotary motion. It has been observed that theunique nesting of diaphragms, the area ratios afforded by the design ofthe piston assembly, and the heights of the cupped pistons are uniquelycombined to provide an actuator having a long stroke in a relativelyshort housing.

Other objects and advantages of the present invention will become moreapparent from the following detailed description of a preferredembodiment thereof and from the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single figure is a schematicsectional view of a pneumatic actuator embodying the features of thisinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As may be seen in the figure, apneumatic actuator embodying the features of the present invention isshown as having a housing indicated generally as 10. The housing isseparated into an upper section 12, a central section 14, and a lowersection 16 for purposes of illustration and ease of assembly. Rod 18 iscentrally located and extends from the upper section 12 of the housinglongitudinally through the housing to the lower section 16 of thehousing and functions as a guide on which the piston assembly indicatedgenerally as 20 slides.

The piston assembly 20 includes an inverted cup piston 22 having arolling diaphragm 24 overlying its upper wall and its peripheral edge 26clamped between abutting flanges of the housing. The diaphragm 24 issecurely retained against the large piston upper wall by the retentionplate 28. A smaller elongated cup piston 30 is disposed in part withinthe large piston and has a rolling diaphragm 32 overlying its lowersurface and the rolling diaphragm 32 is retained by abutting flanges ofthe housing at its peripheral edge 34. The lower diaphragm is securelyretained against the piston 30 by retention plate 36. A central sleeve38 is provided having a shoulder 40 disposed at one end for engaging theretention plate 36 and a nut 42 threaded on the sleeve so that thepiston assembly may be securely locked into a unit. It is evident thatthe sleeve 38 centrally locates the piston assembly over the rod 18 forthe purpose of facilitating longitudinal movement of the piston assemblyon the rod.

Tube 44 may be provided to rigidify the piston assembly. The rod 18 ischrome plated and graphite is embedded in the inner surface of sleeve 38to minimize sliding friction. A tight fit would cause binding betweenthe sleeve and the rod. Seal 46 is provided between the sleeve 38 andthe rod 18 to prevent leakage. The seal is retained withincircumferential groove 48 in the sleeve 38. A diaphragm guide 52essentially cylindrical in shape is interposed between the large and thesmall pistons and projects toward the large diameter piston 22. Thediaphragm guide 52 has an outwardly flaring base 50 disposed betweenabutting flanges of the housing and is retained therein in conjunctionwith the rolling diaphragm 32 associated with the elongated cup piston30. Spring 56 is disposed between the diaphragm guide 52 and theinverted cup piston 22 and bottoms against the housing.

Shoulder 40 on the sleeve 38 has projecting lugs 58 which engage links54 thereby connecting the sleeve to the rotatable shaft 58 through crankarms 60. The rotatable shaft 58 is connected to an actuator valve. Links54 may be replaced by a yoke which straddles the rod 18 and a singlecrank arm may be used.

In operation, controlled servo-pressure is supplied to the chamber 62through the boss 64; and chamber 66 contains supply pressure to whichthe actuator is exposed when mounted at flange 68. As servo-pressure isincreased, the piston assembly slides down the rod into the positionshown in the figure. It is evident that various piston effective areasmay be selected within the scope of this invention. Since the pistonassembly has different effective areas, the pressure in chamber 62required to displace the piston depends upon the piston area ratioselected and can be considerably lower than the pressure in chamber 66.The controlled servo-pressure in.

chamber 62 must also compress spring 56.

In order that the invention will be more easily understood,

sequential operation of the piston will be described. Assuming that theservo-control pressure decreases below that required to maintain thepiston assembly in the lower position, the pres- I sure force over thepiston area of the smaller piston and the force provided by thecompressed spring 56 will translate the piston assembly along the shaft18 to the uppermost position which occurs when the piston assemblyreaches stop '70. The diaphragm 24 is guided by the walls of theinverted large cup piston. The wall length of the large piston shouldexceed one-.-

half the piston travel so that there is sufficient wall length toprovide a support structure for the rolling diaphragm 24 when the pistonassembly is in the uppermost position. Similarly, as

the piston assembly moves upward, the lower rolling.

diaphragm is guided along the inner surface of the cylinder diaphragmguide 52. It is apparent that the diaphragm 32 is not guided by theelongated section 72 of the small diameter cup. The elongated section 72of the small diameter cup is: provided for the purpose of rigidifyingthe piston assembly,

half the stroke of the piston assembly. As the piston assemblytraversesthe rod, it is readily apparent that the links 60 are caused to movethereby causing the pivot bars 60 to rotate the shaft 58. The actuatorprovides at least 90 of rotation and is capable of opening or closingthe valve.

Although the invention has been shown and described with respect to apreferred embodiment, it should be understood by those skilled in theart that various changes and omissions in the form and detail may bemade therein without departing from the spirit and scope ofthisinvention.

lclaim:

l. A pneumatic actuator comprising:

a housing;

means for providing air under pressure to each end of the housing;

a rod extending longitudinally of the housing and fixed to the housingat each end;

a large inverted cup piston having a rolling diaphragm overlying itsupper wall and its peripheral edge fixed to the housing;

a small elongated cup piston disposed in part within the large pistonhaving a rolling diaphragm overlying its bottom wall and its peripheraledge fixed to the housing;

a sleeve concentric with and slidably engaged over the fixed rod, thesleeve having a shoulder disposed at the small cup piston end and havingmeans for coupling the two pistons into a unitary piston assembly at theother end;

a seal disposed between the sleeve and the longitudinal rod;

a cylinder diaphragm guide interposed between the large and the smallpiston projecting toward the large piston;

a shaft rotatably disposed transversely through the housing;

and

a link, engaging a crank on the rotatable shaft and engaging theshoulder of the sleeve whereby axial translation of the piston assemblyconverts to rotary motion of the rotatable shaft.

2. An actuator as in claim 1, wherein the height of the elongated cuppiston is substantially equivalent to the stroke of the piston assembly.

3. An actuator as in claim 2, wherein the height of the large cup pistonand the height of the cylinder diaphragm guide are substantiallyequivalent to one-half the stroke of the piston assembly.

